To clarify: the MySQL "service" is a program that runs all the time, in the background, and its purpose is to carry out the requests that it receives from anyone and everyone.
There's another program, a client program, which is used to submit requests to the service.
So if fifty people are using your MySQL system at the same time:
- There is one copy of the service, running on one computer.
- There are fifty copies of the client-program, each one running on the personal computer of the people who are using MySQL at this moment.
(Notice that I'm assuming that those people aren't, say, using the database through a web-page or something.)
Now, what's the advantage of this?
Whizz-z-z-z-z! Smack! Smoo-o-osh! Oops, incoming meterorite! One of your poor users just got smashed. Or at least his computer did. But fortunately it wasn't the computer that's running the service, so your database was not affected in the slightest. All of the critical operations of actually updating the database files are performed
only by the service, only on that one machine.